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of decreasing wet-edge time limits. Therefore, in this case the addition of butanol to thevarBoiling Range, Varnish Kauri nish decreased the wet-edge time limit. The viss. T. M. ComparaBreakButanol cosity of the varnish a t the wet-edge time limit, Distn., F. tive down Cc. Solvency Co. Initial D ~ Y Spot-Dry N a p h t h a / 5 G. S a p h t h a / i O G. SP. Gr. as well as the percentage of thinner in the varSample b. p. point Time, Hr. Base Varnish K. B. Soln. a t 60’ F. nish a t this point, lay between rather narrow 73.6 325 396 0.25 Mineral spirits 33.4 0.7839 limits. 2 1 . 5 2 8 . 6 0.8100 415 472 2.5y Kerosene 1 b Kerosene 2 371 456 2“ 43 02 .. 15 00 .. 88 31 4482 FILM HOMOGEXEITY. The tests regarding the 96.1 360 500 2.25a Kerosene 3 Kerosene 4 379 502 2.75“ 29.5 29.6 0.8123 homogeneity of the film were qualitative. When varnish in the film a t the wet-edge time limit was a * 15 minutes. b No breakdown a t 200 cc. throughly mixed so as t o become homogeneous, it could be brushed into a fresh varnish film without forming a noticeable junction. If the wrinto be tested was added from a buret until a permanent kling of a film was due to a lack of homogeneity between the cloud was formed. More of a high-solvency thinner could be surface and the rest of the varnish film, it might be inferred added before the cloud point was reached than a low-solvency that the varnish with the larger wet-edge time limit, other thinner. factors being equal, had a greater degree of homogeneity. Kerosenes 2 , 3, and 4 have, roughly, the same distillation Acknowledgment range, but different solvencies; i. e., kerosene 2 has a higher solvency than kerosene 3, which in turn has higher solvency The writers are indebted to C. Hopper for assistance in than kerosene 4. obtaining preliminary data on the wet-edge time limit as PERCEKTAGE OF KEROSENE. The effect of the percentage well as the production of the panels demonstrating the of kerosene used is indicated by a comparison of the following wrinkling of the varnish film. They are indebted to D. Fay pairs: samples 1 and 2, 3 and 4, and 6 and 7 . Each pair and L4.Luetz for laboratory assistance, and wish to acknowlcontained the same type of kerosene. I n the case of the first edge also the helpful suggestions of D. D. Rubek and G. W. two pairs (1and 2 , 3 and 4) the wet-edge time limit decreased Dahl. with an increase of the kerosene percentage. The third pair Literature Cited (6 and 7) indicated that the reverse was true. (1) Gardner, H. rl., “Physical and Chemical Examination of Paints, BUTASOL.The effect of small amounts of butyl alcohol is Varnishes, Lacquers, Colors,’’ 7th ed., pp. 601-7,611,Washingindicated by a comparison of samples 3, 3A, and 3B. These ton, Inst. of Paint & Varnish Research, 1935. samples contained the same thinner mixture of 15 per cent (2) Rubek, D. D . , and Dahl, G. W., IXD.ENG.CHEM.,Anal. E d . , 6, kerosene 2 and 85 per cent mineral spirits. However, in 421 (1934). sample 3A, 2 per cent of the thinner mixture was replaced RECEIVED April 21, 1935. Presented before the Division of Paint a n d Varwith butanol, and in 3B, 3 per cent was replaced with butanol. nish Chemistry a t the 91st Meeting of the American Chemical Society, In Table I samples 3, 3d, and 3B are arranged in the order Kansas City, M o . , April 13 t o 17, 1936. I
TABLE IV. DESCRIPTION OF KEROSESES
*.
Glue Tanning with Formaldehyde Application to the Manufacture of Hectograph Masses ERIK R. NIELSEN The Miner Laboratories, Chicago, Ill.
T
HIS investigation was carried out during the development of a new process (2) for the manufacture of hectograph masses. A hectograph mass is essentially a glue-glycerol-water composition to which small quantities of other compounds are usually added for hardening, preserving, and pigmenting the composition. The old-fashioned pan hectograph has largely been replaced by the hectograph roll-that is, a hectograph copying surface in roll form, adapted for use in special machines which permit speed in copy-taking. The roll is unwound in the machine, section by section, over a copying platen, a fresh section being used for each different master. The rolls are long (about 16 feet) to permit the copying of several masters without change of roll. As the roll leaves the platen, it is rewound; on the following day the roll should have absorbed the excess ink so that it may be used over again.
Analyses of a number of rolls of different manufacture showed that they were hardened or tanned (at least in part) with formaldehyde. Figure 1 gives the melting point curves for a number of these rolls. Some were fresh or “green” when purchased-that is, only slightly hardened, as indicated by the low melting points. Such rolls were At, Aa, Ag, B, Cz,and D. Other rolls were already considerably tanned at the time of purchase, such as AI, A d , and C1. Curve A , represents the untanned composition obtained from one manufacturer.
Experimental evidence is offered which indicates the advantages of adjusting the pH between 7 and 9 in the preparation of glue-glycerol-formaldehyde compositions of predetermined melting point. The effects of certain other factors involved in this reaction are also reported.
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VOL. 78. NO. 8
rolls, it became e\ d e n t that the rolls were unsatisfactorily hardened since they continued to change in their essential characteristics after they had reached the consumers. It was therefore decided t o attempt the development of a hardening process by which a hectograph mass could be quickly cured to give a product of pretleterinined and constant melting point.
Literature S o report was discovered on the actual tanning of hectograph masses. The general literature on the subject of tanning gelatin gels contains the following pertinent information: External treatment of a gel with formaldehyde does not result in uniform tanning, and the rate of tanning is proportional to the quantity of formal4 8 /2 id PO 2? Number @/Yonths snce rme ofPurchose offhe Hectcgruph E c k dehyde used (1). The reaction between gelatin and formaldehyde FIGERE1. MELTING POIKT CURVES FOR HECTOGRAPH COMPOSITIOX5 does not proceed rapidly; in other words, progresA , B , C, D indicate the four manufacturers from whom t h e rol!s were purchased. sive hardening takes place (3). Formaldehyde n-ill combine with gelatin from a solution as acid as pH 4, but the best reaction takes place betneen pH 6 and 9; above pH 9 the ie-ults are much poorer (4). Rolls from the same manufacturer varied consideraliy in melting point even when purchased at the saine time. Thuq The statement that the best reaction takes place between rolls C1 and Cz \\-ere purchased on the same date froni m e p H 6 and 9 TVXS not found to apply t o hectograph masses, a t manufacturer and were claimed to have the same kind of 1ea.t not in the case of sinal1 quantities of formaldehyde. copying surface; the only difference was that one had a fiber The reaction takes place most efficiently between pH 7 and 9, and the other a cloth backing. The melting points, hon ever. and the results obtained within this range are far superior to were far apart (Figure 1). those obtained a t a p H even slightly below 7 . This is shown The perforniance of a roll and the degree of hardening it has in Figure 2 where the results of tanning a t p H 6.4 are comreceived (as measured by the melting point) are closely repared with those obtained a t p H 7 , 8, and 9. lated. A "green" roll gives bright initial copies; but a. the The tanning process was studied in respect to the following copy-taking progresses, the brightness and strength of the factors: ( 0 ) the quantity of formaldehyde used, (b) the p H copies decrease rapidly. This type of roll would be ideal for value of the composition to be tanned, (c) the temperature jobs requiring only a few, bright copies. Unfortunately .uch conditions during the cure of the composition, and ( d ) starolls disintegrate rapidly during use, especially in hot and bility of tanned compositions humid l\-eather. If the degree of tan is raised. the character of the obtainable copies changes in that the copies tend to hecome more uniform; the later copies gain in strength at the expense of the initial ones. Rolls within a melting point range of 65" to 75" C. still give bright copies and yet are sufficiently hardened to stand u p in hot, humid weather. As the degree of tan is still further increased, the brightness of the initial copies gradually decreases, but the copies as a whole become more uniform and the number of legible copies increases accordingly. The degree of tan should, however, not be greater than that indicated by a melting point of about / 80" C. Otherwise the strength of the copy suffers too much. All the commercial rolls studied showed progressive hardso Age 01 C o m p o/GO s~hn/n Doys /so ening during storage (Figure l),and the majority hardened excessively, reaching melting points of 100" C. and higher. FOR HECTOQRAPH COMFIGURE 2. MELTISG POINTCERVES POSITIOSS COST.4IXIiYG 0.045 P E R C E N T FORMALDEHYDE, AT A few rolls showed only moderate hardening even after long VARIOUSPH VALUES storage, but the rate of hardening in these cases was very slow; several months of storage were necessary before the melting points of such rolls were within the safe range for use in the hot summer months. Such rolls were A6 and C:! (Figure 1); they were cloth-backed, whereas the other rolls were fiber-backed. I n the preparation of the fiber backing, it seems to be customary in some plants t o saturate the paper base with a glue-glycerol mixture and to draw the saturated paper through a bath of more or less dilute formaldehyde solution. The base is dried and then lacquered on one side. T o the unlacquered side, the hectograph mass is applied. It is reasonable to assume that such a fiber backing contains unSO Me i50 1 reacted formaldehyde which diffuses into the hectograph Age QtCompcs/f/on /n Days mass and tans it. This assumption woiild explain the exceisive tanning of the fiber-backed rolls. FOR HECTOGRAPH COMFIGURE 3. MELTINGPOISTCURVES At an early date in this study of commercially available POSITIONS OF ORIGISAL PH (6.4) I
I
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Experimental Methods In order to simplify the interpretation of the esperiment,al results, all the tanning experiment's were carried out on the same standard composition-that is, 10 per cent glue. 65 per cent of 95 per cent glycerol, and 25 per cent water. The jelly strength of the glue used in the experiments was 237 grams (Bloom gelometer), and the viscosity was 67 niillipoises according to the methods of the Sational Association cf Glue Manufacturers. I n dissolving the glue, part of the water was always kept out in order to be able to add the formaldehyde in dilute solution (1 per cent) and still adhere to the standard formula for the composition. Test samples were prepared by pouring the liquid composition onto suitable backings to form layers of a uniform thickness. The samples were always stored in closed containers with a minimum of air space so as to prevent significant moisture losses during storage. The tanning process was followed by determining the nielting point of the samples from time to time in the follon-ing manner: A 1 . 5 X 1.5 cm. square was cut from the sample and reiiiol-ed from the hacking. h 14-gage wire was passed through the center of the square in order to suspend it in a vessel filled n-ith white mineral oil. The distance from the center of the square t o the bottom of the vessel was always kept the same-that is, 4 mi. T h e oil was heated so as to obtain a 1' C. rise every 30 seconds. I n the case of a n untanned or only slightly tanned sample, the square left the wire a t a certain temperature and immediately fell t o the bottom. I n the case of higher tans. hon-ever, the square gradually lost shape and stretched toward the bottom of the vessel. With nioderate tans the sample left the wire before the bottom was reached. With higher tans the square stretched to form a string, the end of which reached the bottom before the sample left the wire. 3-unierous tests showed t h a t in t h e case of highly tanned samples the best reproducible temperature was t h a t at which t h e sample reached the bottom. and it was therefore decided to define the melting point of a n y sample as the temperature a t which the sample scluare n-ould rearh the bottom under the conditions described.
Effect of Formaldehyde Concentration on Tanning Rate and Degree Saiiiples of standard coniposition were tanned with 0.05, 0.07, and 0.08 per cent formaldehyde, based upon the weight of the composition (or with 0.5 to 0.8 per cent based upon the weight of the glue). The test samples were poured immediately after the addition of formaldehyde. The tanning process was followed by taking the melting points. The melting point curves are shown in Figure 3 . These curves show that the rate of hardening and the degree of tan obtained were proportional to the quantity of formaldehyde used and also that the tanning process under those conditions (which might well be termed the "ordinary" ones) was a slowly progressing reaction. These results checked those obtained by Reiner (3) and also the writer's observations on commercial rolls, shorn-n in Figure 1.
Effect of pH Value on Tanning Rate and Degree Samples of standard composition were tanned with 0.045 per cent formaldehyde (based upon the weight of the glue), but each sample was adjusted to a different p H value. The quantity of sodium hydroxide necessary to produce the desired p H value was added in advance of the formaldehyde, and the test samples were poured immediately after the addition of formaldehyde. The melting point curves for these conipositions are shown in Figure 2 . The sample of pH 6.1 m-as used as an unmodified control. The curves shov that the rate of tanning was proportional to the increase in pH, the change being most pronounced when passing through the neutral point. The curves also show that the degree of tan obtained mi proportional to the increase in pH. It is evi-
FIGURE 4. MELTINGPOISTCCRVES FOR HECTOGRAPH COMPOSITIOSS TASNED WITH 0.045 P E R C E K T FORM.4LDEHI.DE, .4T VARIOVS PH VALUES A
T e ~ samples t poured immediately after formaldehyde addition.
B. Compositions maintained a t 60' C. for 4 hours a f t e r formaldehyde addition before test samples were poured.
dent that a quick-curing conipo3itiun of predetermined nielting point may be prepared by chooqing the proper pH and formaldehyde concentration.
Effect of Temperature o n Cure An increase in temperature was expected to accelerate the rate of tanning. Two series of samples were prepared. I n both series the samples were tanned with 0.045 per cent formaldehyde, but the p H was adjusted to different values within each series. I n one series the compositions were maintained a t 60" C. for 4 hours after the addition of formaldehyde, and then the test samples were poured. I n the other series the test samples were poured immediately after the addition of formaldehyde. The melting point curves for the samples in both series are shown in Figure 4. Contrary to expectations the heat-cured samples showed much lower melting points than the samples which had not been kept hot after the addition of formaldehyde. That this difference was not due to hydrolysis of the glue when the compositions were kept liquid and hot for 4 hours was shown in a separate series of experiments. I n this series, samples of standard composition were adjusted t o different pH values, but no formaldehyde was added. For each p H value test samples were poured immediately after the adjustment of the p H and again after holding t h e conipositions for 4 hours a t 60" C. The melting points of these untanned samples, one week after their preparation, are as follows: PH
Sample Poured Immediately after Preparation
6.4 8.0 0.0
42 42 1?
Sample Poured after Holding 4 H r a t 60' C.
c.
C'.
41 40 89
It is evident that the small decrease in melting point due t o hydrolysis of the glue cannot explain the great differences shown in Figure 4. That the differences were not due to loss of formaldehyde by evaporation in the case of the heat-cured samples was shown in a separate series of experiments in which the heat-cured samples were kept in completely filled and closed pressure bottles. The melt'ing points of these and of the control saniples poured immediately after the addition of formaldehyde are as follon-s:
---_ \I. 1 neek
c.
Sample poured immediately after prepaiation Sample poured after holding 4 hr. a t 60' C . in completely filled and closed pressure bottles a
P.n
after:-2 weeks
c.
88
92
52
56
For Compositions tanned with 0.045 per cent formaldehyde a t p H 8 .
INDUSTRIAL AND ESGISEERISG CHEMISTRY
946
Sotwithstanding, the great difference in iiieltiiig points shown by Figure 4, it is believed that heating actually accelerated the reaction between the glue and the formaldehyde. At temperatures below the setting point of the fresh coniposition the rate of tanning is proportional to the storage teniperature. I n order to show this behavior, samples of the same composition were stored a t different temperatures. In one experiment the p H of the standard composition was adjusted to 8.3, and 0.035 per cent formaldehyde was added. The test samples were poured immediately and half of them were stored a t 10-15' C.; the other half were stored at 25-30' C. The melting point curves for these samples are shown in Figure 5 . These results were checked with other compositions and indicated that, within the range studied-that is, below the melting point of the gel--the rate of t'anning increased with the temperature. s hTo hwen dby i f f Figure e r e n c e4s
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and showed measurable decreases in melting point, ranging from 10 to 30 per cent depending upon the concentration of formaldehyde and the original pH value. Such a gradual change is not serious when the alkaline tanning process is applied to hectograph compositions; the composition ordinarily IYill have been used up long before there is any apparent change, and in addition this gradual change in p H offers a certain advantage. The use of high alkalinity a t the time of tanning makes it possible to reach equilibrium quickly and, if during storage the pH is gradually reduced, it is possible to use a higher initial p H than would otherwise have been safe for fear of hydrolyzing the glue. However if such a change is undesirable, it means simply that noncarbonating alkaline agents must be used for the pH adjustment. I n a further study of the relation of the pH to the stability of the composition, experiments were carried out as follows: I n one case a composition was investigated which had been tanned with 0.02 per cent formaldehyde a t an initial p H of 8.6. Different samples of this composition were washed with phosphoric acid (1, 5 , and 10 per cent solutions). After one week the melting points and pH values were determined on the different samples. The results of these determinations are as follom:
Fo: 3
must be explained as t h e d i f f e r e n c e between curing in t'he 0 Currot:0-,.5?L2 l i q u i d a n d the gel !5 !/O 1 /5 L eng/h o/ Cure /oDu?/s state. In support of this theory the folloivFIGURE 5. MELTINGPOIKT CURVES ing experilllellt was FOR SAMPLES OF THE SAME COMPOSITION CURED UNDER DIFFERENT made: Samples taken CONDITIONS from a tanned standa r d composition (melting point, 71 " C.) m-ere suspended on a wire in an oil bath and heated. As usual in the case of a tanned composition the pieces formed strings which eventually reached the bottom of the bath. After this condition had been reached, the mire was lifted from the bath. Part of the material (in stringy form) followed the wire; the other part remained at the bottom and was collected. Both parts were cooled to room temperature, and the melting points were determined the following day. The material remaining a t the bottom showed a melting point of 43" C., practically like that of an untanned composition. The stringy material showed a melting point of 65" C., only slightly lower than that of the composition used for the experiment. This experiment Tyas repeated on other tanned compositions with similar results. These experiments seem to indicate that a tanned composition actually was a mixture of tanned and untanned or only slightly tanned material, such as might be expected if the structural or honeycomb theory of tanning was valid. It was also found that the melting and repouring of a tanned composition produced a material which had a melting point only slightly above that of an untanned composition; this fact could also be explained by the honeycomb theory, since the melting of the sample would destroy the honeycomb structure and therefore the resistance of the gel towards melting. Thus, in the case of a composition melting a t 111' C., a sample was melted and again allowed to solidify. Two days later the melting point of the solidified material was found to be only 45' C. c Cure otC'5-30'C
$ st
% H~POI
PH
Sone
8.0 8 0 4.0 Belox 3
1
5 10
1 2 P., 73
c.
65 58 50
These results indicate that the melting point of a tanned composition is a function of its pH, or that the equilibrium of the formaldehyde-glue reaction is dependent. upon the pH of the reaction medium. Similar experiments checked these result s.
Advantages of the Process The principal advantages of using the described tanning process in the manufacture of hectograph rolls are as follows: I t makes possible the manufacture of a roll with predetermined copying characteristics, whereas the ordinary roll changes in copying characteristics during its whole life. Various types of rolls may be manufactured to meet specific demands, such as rolls giving a few, bright copies or those giving many but not such bright copies, or rolls for summer or winter use. The process makes it possible to manufacture rolls during the warmest weather since the composition tans so fast that .the rolls, after an overnight cure a t low temperature (about' 60" F.), are sufficiently hardened to withstand even summer weather.
Literature Cited (1) Ahegg, R . , and von Schroeder, P., Kolloid-Z., 2, 85 ( 1 9 0 7 ) . (2) Nielsen, E. R., U. S. Patent 1,938,927 (Dec. 12, 1 9 3 3 ) . (3) Reiner, KoZIoid-Z., 27, 195 ( 1 9 2 0 ) . (41 Thomas, A. JT,,et al., J . -4m Leather Ciiem. dssoc., 21, 57 (1926). RECEIVED January 22, 1936.
Stability of Tanned Compositions With the tanned alkaline compositions prepared with SOdium hydroxide, there is a tendency for the alkali to become carbonated. I n view of the fact that only a small part of the sodium hydroxide is surface-exposed, this carbonation takes place slowly. The carbonation is followed by a change in pH, and this in turn by a change in melting point. The latter change is very gradual. With the alkaline compositions described (Figure 4), a constant melting point was obtained in about 21 days and the melting point then remained constant to the end of the observation period-that is, 160 days. After two years of storage these samples were again checked
Correction Owing to a regrettable oversight in the article "Changes in Whisky during .4ging" [IND.ENG.CHEM., 28, 302-4 (1936)1, credit for the chemical analyses was not given to A. Herman, chief chemist of Seagram Distillers Corporation, at whose euggestion the work was undertaken, gratuitously. F. E Ray CINCINNATI, OHIO June 1 1 , 1936
